In this stunning close-up of Messier 45 (The Pleaides) three of its brightest stars are clearly visible. In the top centre we see Alcyone, an eclipsing binary system. In the bottom right corner we see Maia, a blue-white giant. It is one of the stars surrounded by the emission/reflection nebula NGC 1432, also known as the Maia Nebula. The bright star to the left is Merope, a blue-white subgiant. It is the central star in the Merope Nebula, a nebula through which the Pleiades cluster is currently passing.

Reflection nebulae reflect light from a nearby star. In the Merope Nebula, many small carbon grains reflect the light. The blue color typical of reflection nebula is caused by blue light being more efficiently scattered by the carbon dust than red light. The brightness of the nebula is determined by the size and density of the reflecting grains, and by the color and brightness of the neighboring star(s).

It is long thought that the dust in the reflection nebula is the remnant of the cloud that the Pleiades formed from, but it is now known that the Merope Nebula is caused by a chance encounter between the open cluster of stars and the interstellar cloud it is plowing into.

The Merope Nebula contains a bright knot – designated IC 349 and also known as Barnard’s Merope Nebula, after the American astronomer E. E. Barnard who discovered it in 1890 – which lies at only 0.06 light-years distant to the southeast of Merope (seen in this image as the white, fluffy dot that almost sticks to the left side of the star). IC 349 is naturally very bright but is almost hidden in the radiance of Merope.